The present invention relates to a heating drum for receiving, respectively winding thereon, a printing blanket to be vulcanized in a pressure chamber, whereby the printing blanket is provided with a cover layer of elastomeric material.
The quality of printing blankets has to meet increasingly stringent requirements in order to provide flawless printing products.
It has been known to wind the preconfected printing blanket blank onto a heating drum and to vulcanize the coiled printing blanket in a pressure chamber.
However, it has been shown that the sensitive printing blankets often have defects in their cover layers after the vulcanization step due to imprints of the contacting points (where the leading edge of the printing blanket rests on the heating drum) of the printing blanket coil. Furthermore, the surface relief or stamping generated by the commonly provided relief cardboard, wound together with the printing blanket onto the heating drum, is stronger in the inner windings than in the outer windings of the coil.
The imprints generated by the contacting points and the reliefs or stampings generated by the relief cardboard with differing strengths from the inside of the coil to the outside are a result of the vulcanization of the printing blanket coil causing a higher pressure tension in the interior of the coil because the great heat expansion of the heating drum and the coil during the vulcanization step increases the inner pressure of the printing blanket coil. The increase of the diameter of the heating drum causes an increased imprint of the contacting point in the first few windings of the printing blanket which necessitates discharge of these first windings because they are unsuitable for printing.
It is therefore an object of the present invention to provide a heating drum of the aforementioned kind with which it is possible to minimize detrimental imprints and reliefs of varying strength.